A pastor and at least 20 worshippers were killed when gunmen suspected to be Islamist militants opened fire in two separate incidents targeting worship services in northern Nigeria Sunday.

In the first attack, gunmen in the northern city of Kano targeted an area in the Bayero University campus where churches hold Sunday services, killing at least 16 people and wounding more than 22 others, The Associated Press reported, quoting an account by the Nigerian Red Cross.

Kano state's police commissioner, Ibrahim Idris, said the gunmen entered into the campus on motorcycles and threw small explosives made out of soda cans around the area inside Bayero University. The worshippers tried to escape but gunmen opened fire. "By the time we responded, they entered [their] motorcycles and disappeared into the neighborhood," Idris was quoted as saying.

Later on Sunday, gunmen in the northeastern city of Maiduguri shot at worshippers inside a chapel of the Church of Christ in Nigeria, killing the pastor who was preparing for Communion and four congregants. The attack took place near a mosque that was formerly used by the country's most notorious Islamist group Boko Haram.

Witnesses said the gunmen stormed into the church service and began firing at the worshippers as they tried to hide or flee. When the worshippers came back, they found the pastor and four others dead in a pool of blood.

The attacks came just a day after Nigerian President Goodluck Jonathan vowed to crush Boko Haram by the end of June. "Just like a war situation, you may dialogue, you may not dialogue, depending on the circumstances. But we will exploit every means possible to bring this to an end," the president told reporters Saturday.

Boko Haram, which means "Western education is sin," has been seeking to exploit tensions between sections of Muslims and Christians to make a case for the secession of the Muslim-dominant north from the largely Christian south.

The actual name of the group is Jama'atul Alhul Sunnah Lidda'wati wal jihad, which translates as "people for the propagation of the prophet's teachings and jihad." Mohammad Yusuf, the Islamist cleric who formed the group about a decade ago in Maiduguri city, was against Western education. Yusuf was from the Salafi movement, which has fueled jihadist terrorism in several parts of the world as a legitimate expression of Islam.

It is believed that Boko Haram has gained technical sophistication and weaponry with help from groups like al-Shabaab in southern Somalia and al-Qaida in the Islamic Maghreb. The terror group, which also targets police and Muslim civilians, has warned that all Christians living in the north should move to the south unless they want to be killed.

Boko Haram's attacks escalated and Christians became one of the primary targets after the victory of President Jonathan, a Christian from the south and a leader of the People's Democratic Party, in the April 2011 election.